The present invention relates to a device for determining the vertical direction of a system which is supported on a moving base, for instance a craft, a vehicle, an aircraft, a ship, or the like.
The invention can be applied advantageously to a weapon system which is to be stabilized on a vehicle, and therefore, in the following, will be described with reference to such an application. However, it is obvious that the invention is not limited to such a weapon system, but can be applied generally when the vertical direction in relation to a moving base is to be determined.
When determining the vertical direction in relation to a moving base it is a common practice to use a so-called vertical gyro, which comprises a gimbal mounted gyro, the spin axis of which is directed vertically. When this vertical direction once has been established, and the gimbal mount of the gyro is free from friction, the vertical direction of the spin axis is retained, regardless of the position of the base. As a rule, the position of the base in relation to the vertical direction is determined by measuring two angles, the so-called roll and pitch angles. Conventional vertical gyros vary as regards the method of compensating for the unavoidable gyro drift, static and dynamic accuracy and the like. A common feature of vertical gyros is that they comprise gyros mounted in gimbals, the mechanical design of which is rather complicated. It has therefore, in other applications, been attempted to use velocity-sensing gyroscopic sensors instead, for instance rate gyros, which in relation to conventional, two-axis gyros have the important advantage that the manufacturing cost will be considerably lower. This is due to the fact that gyroscopic sensors have a simple mechanical design, with only one sensitive axis.
When a weapon which can be elevated and traversed is to be stabilized, that is, when the aiming of the barrel of the weapon is to be made independent of movements of the base, information is required in regard to the rotating movements around two axes. It is previously known to measure the rotating movements with gyroscopic sensors which measure the turning velocities of the weapon in elevation and traverse.
When the weapon is included in a weapon system which also comprises fire control equipment with at least one aiming telescope and one calculator, however, information is also required in regard to the turning angle of the elevation axis around the direction of the barrel from the vertical plane, and also often the angle of the direction of the barrel towards the horizontal plane. The conventional designation of these angles is the roll and pitch angle, and in the following this designation will thus be used. The most common method hitherto used of measuring these angles has been with the aid of the conventional vertical gyros.